High Acid Density Research Articles

Sulphonated Carbon Dots Synthesized Through a One‐Pot, Facile and Scalable Protocol Facilitates the Preparation of Renewable Precursors Using Glucose/Levulinic Acid

AbstractHerein, we report the efficacy of Brønsted acid‐functionalized CDs in an enriched preparation of 5‐hydroxymethylfurfural (HMF) and ethyl levulinate (EL) energy fuel building‐block compounds. The cheap p‐toluenesulphonic acid was used as a precursor to prepare CD‐SO3H by employing a simple, one‐pot and scalable protocol. The high‐end analytical techniques endorsed the catalyst's higher acid density and minimum particle size characteristics. Its glucose reaction evaluation resulted in an 82 mol% HMF using glucose via dehydration. Similarly, it enabled an 85 mol% EL from levulinic acid via esterification under modest reaction conditions. It also promoted the synthesis of other varieties of alkyl levulinates (such as levulinic acid 1‐butyl and methyl esters) with a similar yield result. The recyclability study showed that it could be reused for up to 5 cycles. Overall, the catalytic setup represented an environmentally‐friendly and feasible method for process development.

Hierarchically Ordered Porous Solid Acid: Preparation and Application as a Biodiesel Catalyst

AbstractAcid‐catalyzed esterification of high fatty acid content feedstocks with methanol is an efficient way to prepare biodiesel. In this work, using the dual template method combining the colloidal crystal template and the porogen, a series of hierarchical ordered porous weak cross‐linked polystyrene solid acid catalysts with high mass transfer efficiency and high acid density were successfully prepared. This catalyst displayed stronger acid strength and better swelling properties. The specific surface area of the obtained catalyst is 32 m2 ⋅ g−1, and its acid value reaches 4.11 mmol ⋅ g−1. The effect of the hierarchical porous structure and swelling on the access to the catalytic sites were illuminated. Acid‐catalyzed reactions showed that hierarchically ordered porous cross‐linked polystyrene solid acid catalyst was more active (the efficiency of the esterification of oleic acid and methanol was up to 93.67 %) than Amberlyst‐15 catalyst.

Chain-like ZSM-5 zeolite coupled with Cu-Fe3O4 for CO2 hydrogenation to light aromatics

The capture and utilization of carbon dioxide (CO2) have attracted much attention in recent years; in particular, the direct hydrogenation of CO2 to light aromatics has been considered as a potential route to produce high value-added chemicals. However, it is still a big challenge to adjust the aromatic distribution and achieve a high selectivity to the targeted products. In this work, a bifunctional catalyst that combines the Cu-modified Fe3O4 and the chain-like ZSM-5 zeolite is used for the hydrogenation of CO2 to light aromatics. The catalyst components were characterized by XRD, SEM, TEM, ICP-AES, Py-IR and N2 adsorption-desorption; the effect of acid density and length-to-diameter ratio (b-axis/a-axis) of zeolite moiety on the selectivity and distribution of aromatic products was then investigated. The results indicate that the chain-like ZSM-5 zeolite moiety with high acid density and appropriate length-to-diameter ratio can promote the C–C coupling for CO2 hydrogenation and inhibit the formation of CH4, which can improve the selectivity to aromatics and the space time yield (STY) of toluene.

Efficient Production of Biodiesel Catalyzed by Acidic Nanoporous Carbon Materials: A Review

Background: With the gradual decrease in fossil energy, the development of alternatives to fossil energy has attracted more and more attention. Biodiesel is considered to be the most potent alternative to fossil energy, mainly due to its green, renewable, and biodegradable advantages. The stable, efficient and reusable catalysts are undoubtedly the most critical in the preparation of biodiesel. Among them, nanoporous carbon-based acidic materials are very important biodiesel catalysts. Objective: The latest advances of acidic nanoporous carbon catalysts in biodiesel production was reviewed. Methods: Biodiesel is mainly synthesized by esterification and transesterification. Due to the important role of nanoporous carbon-based acidic materials in the catalytic preparation of biodiesel, we focused on the synthesis, physical and chemical properties, catalytic performance and reusability. Results: Acidic catalytic materials have a good catalytic performance for high acid value feedstocks. However, the preparation of biodiesel with acid catalyst requires relatively strict reaction conditions. The application of nanoporous acidic carbon-based materials, due to the support of carbon-based framework, makes the catalyst exhibit good stability and unique pore structure, accelerates the reaction mass transfer speed, which in turn accelerated the reaction. Conclusion: Nanoporous carbon-based acidic catalysts have the advantages such as, suitable pore structure, high active sites, and high stability. In order to make these catalytic processes more efficient, environmentally friendly and low cost, developing new catalytic materials with high specific surface area, suitable pore size, high acid density, and excellent performance would be an important research direction for the future biodiesel catalysts.

An excellent sulfonated hydrothermal carbon catalyst from Mangifera indica L. (mango peels) for biodiesel production: preparation, characterization, optimization, and kinetic study

The current study describes the preparation and catalytic activity evaluation of newly synthesized hydrothermal carbon catalysts for biodiesel production. The catalysts (HTCC-M2-10h) were prepared through the sulfonation of mango peels (Mangifera indica L.) using concentrated sulfuric acid at various time intervals from 2- to 10-h process. The catalysts were characterized via sophisticated analytical techniques to analyze surface area, functional groups, morphology, and acid density sites. The catalyst prepared at a 6-h time interval shows a high density of proton switchable/acidic sites attached to the carbon surface (i.e., SO3H, COOH, and OH). The catalyst was found to exhibit a large surface area (42.13 m2/g), well-ordered porosity, and large pore volume. The catalytic activity was determined by examining the catalyst performance for fatty acid esterification to produce the methyl ester (i.e., biodiesel). Thus, HTCC-M6h (prepared at 6 h) gives the maximum catalytic activity due to its high acid density (3.46 mmol/g) and large surface area. The maximum 98.6% oleic acid conversion into methyl oleate was obtained at 65 °C by using 10:1 v/v methanol:oil and 5 wt% of catalyst within 4 h. The kinetic study for oleic acid esterification by HTCC-M6h performed at temperatures between 40 and 70 °C confirmed the first-order reaction as is the case for homogeneous esterification reaction. The recyclable ability of catalyst was also determined and found that the catalyst has enough potential to recycle up to four times without any reactivation step and any activity loss after that catalyst can be regenerated. The results revealed that the HTCC-M6h exhibits high stability, high catalytic activity, and reusability. It could be concluded that the prepared HTCC-M6h will prove itself an innovation in heterogeneous catalysis.

Polymeric ionic liquids (PILs) with high acid density: Tunable catalytic performance for biodiesel production

A series of polymeric ionic liquids (PILs) used as effective heterogeneous catalysts for biodiesel production via esterification of free fatty acids (FFAs) were effectively prepared by the reaction of poly (ethylene imine) (PEI) polymers with different molecular weight and 1,3-propanesultone, followed by the further acidification with differential effective acids, i.e. H 2 SO 4 , CF 3 SO 3 H, CH 3 SO 3 H or p -toluenesulfonic acid ( p -TSA). Ultrahigh acidity and catalytic performance were achieved and could be fine-tuned by simply adjusting the molecular weight of PEI and by further treatment of acids. Specifically, under the optimal conditions ( i.e. reaction temperature was 70 °C, reaction time was 2.0 h, catalyst dosage was 3.15% (mass), and alcohol/acid molar ratio was 14:1) acquired through the Box-BEHNKEN response surface methodology, a high oleic acid conversion of 98.42% could be obtained over the optimal PIL, PEI(70000)-PS- p -TSA. Additionally, our PILs also showed high generality for esterification of other FFAs, with general high conversion over 90% noted in each case even under much milder reaction conditions compared to other conventional catalysts.

Highly efficient conversion of glucose to methyl lactate over hierarchical bimetal‐doped Beta zeolite catalysts

AbstractBACKGROUNDMethyl lactate is widely applied in the chemical, food, cosmetics and pharmaceutical industries. The conversion of carbohydrates over heterogeneous catalysts to methyl lactate is a promising environmentally benign process.RESULTSHierarchical Sn‐Beta zeolite (Sn‐Beta) and corresponding bimetal‐doped Beta zeolites (M‐Sn‐Beta; M = Zn, In, La, Ga, Ni) were prepared via a novel modified hydrothermal synthesis method to convert carbohydrates into methyl lactate. The introduction of Zn into Sn‐Beta considerably improved the yield of methyl lactate from glucose, while for the catalysts containing In, La, Ga and Ni, such improvements were not observed.CONCLUSIONSA methyl lactate yield reaching up to 66.7% was obtained over Zn‐Sn‐Beta at 220 °C for 6 h. The enhanced catalytic performance was attributed to high Lewis acid density and strength, together with synergistic effects between framework Sn4+ and Zn2+ ions of Zn‐Sn‐Beta. Additionally, Zn‐Sn‐Beta demonstrated fructose and sucrose conversion into methyl lactate with yields of 68.4% and 70.0%, respectively. The Zn‐Sn‐Beta catalyst could be re‐used at least five times with only a slight loss of methyl lactate yield. © 2021 Society of Chemical Industry (SCI).

Incorporation of Al3+ Sites on Brønsted Acid Metal-Organic Frameworks for Glucose-to-Hydroxylmethylfurfural Transformation.

5-hydroxylmethylfurfural (HMF) is a bio-based chemical that can be prepared from natural abundant glucose by using combined Brønsted-Lewis acid catalysts. In this work, Al3+ catalytic site has been grafted on Brønsted metal-organic frameworks (MOFs) to enhance Brønsted-Lewis acidity of MOF catalysts for a one-pot glucose-to-HMF transformation. The uniform porous structure of zirconium-based MOFs allows the optimization of both acid strength and density of acid sites in MOF-based catalysts by incorporating the desired amount of Al3+ catalytic sites at the organic linker. Al3+ sites generated via a post-synthetic modification act as Lewis acid sites located adjacent to the Brønsted sulfonated sites of MOF structure. The local structure of the Al3+ sites incorporated in MOFs has been elucidated by X-ray absorption near-edge structure (XANES) combined with density functional theory (DFT) calculations. The cooperative effect from Brønsted and Lewis acids located in close proximity and the high acid density is demonstrated as an important factor to achieve high yield of HMF.

Preparation and characterization of biomass-based nanocatalyst for hydrolysis and fermentation of catalytic hydrolysate to bioethanol

In this study, magnetic solid acid nanocatalyst was synthesized using Syzygium cumini seed powder and green synthesized magnetic Fe3O4 nanoparticles by wet impregnation method. The catalyst with a high acid density of 0.85 mmol g−1, the surface area of 466.905 m2 g−1, and pore volume of 0.191 cm3 g−1 was obtained. The prepared nanocatalyst Fe3O4–@C–SO3H was used to hydrolyze ultrasonic pretreated palmyra peel and corncob biomass in a magnetic stirrer. The total reducing sugar (TRS) of 97.6% and 90% was achieved for palmyra peel and the later for corncob under varied conditions of catalyst concentration and temperature. It is observed at 0.3-g catalyst concentration and 125 °C temperature gave the best yield for the palmyra peel sample within 1 h. And for corncob samples at 0.2-g catalyst concentration and 135 °C gave the best sugar yield within 1 h. The hydrolysate comprising high reducing sugar was further fermented using Saccharomyces cerevisiae. Bioethanol yields of 78.3% from palmyra peel and 62.7% from corn cob were quantified using gas chromatography technique.

Synthesis of a novel bifunctional mesoporous Ti-SBA-15-SO3H catalyst and studies on their enhanced performance and kinetic modeling of lactic acid esterification reaction with n-butanol

Abstract In the present study, the mesoporous Ti-SBA-15-SO3H catalyst is synthesized by using the sol-gel method. Further, these materials have been characterized by different advanced analytical techniques such as Low angle X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Thermogravimetry/Differential thermal analysis (TG/DTA), N2 adsorption/desorption studies, Fourier transform infrared spectroscopy (FT-IR), UV–Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), Temperature-programmed desorption of ammonia (NH3-TPD) and Lactic acid esterification catalytic activity studies. The Ti-SBA-15-SO3H catalyst is found to have a surface area of 457 m2/g, a pore volume of 0.12 cm3/g, a pore diameter of 3.16 nm, and a high acid density of 1.72 mmol/g. The optimum reaction conditions for lactic acid esterification with n-butanol are found to be a 1: 4 M ratio, 3 wt-% catalysts, 115 °C temperature, and 120 min reaction time to obtain 72% conversion. Further, the reusability tests reveal that the spent catalyst can be used for five successive runs without the loss of considerable activity. The pseudo-homogeneous model was able to describe the kinetics of this esterification with negligible error. The activation energy and equilibrium rate constant for Ti-SBA-15-SO3H is found to be Ea = 0.063 KJ/mol and K = 5.019 lit/mol min, respectively, to catalyze the esterification of lactic acid with n-butanol. A plausible mechanism for the catalytic activity is proposed.

Phosphotungstic acid on activated carbon: A remarkable catalyst for 5-hydroxymethylfurfural production

Phophotungstic acid (HPW) supported on activated carbon (AC) was prepared and used for dehydration of fructose to 5-hydroxymethylfurfural (HMF), a biomass-derived precursor for chemicals and fuels. Different characterization techniques showed that Keggin structure of HPW was maintained after impregnation process by incipient wetness method with ethanol as solvent. The high mass content of the active phase (50 wt%) on the support resulted in accessible acid sites and high acid density, important for the dehydration reaction. The effects of reaction time, catalyst amount, and temperature were investigated. The catalytic system with dimethyl sulfoxide (DMSO) as solvent provided an efficient transformation of fructose to HMF, resulting in high HMF yields (99.3 %) and total fructose conversion after 30 min of reaction at 140 °C. Fructose conversion was not significantly affected by the catalyst amount. On the other hand, the increase in temperature resulted in greater and faster conversion. HMF yield was deeply affected by all reaction variables. Moreover, HPW/AC was reused five times without significant loss of activity. Additionally, a kinetic evaluation was performed and the activation energy of fructose conversion to HMF was 109.4 kJmol−1.

Preparation of Hydrophobic Acidic Metal–Organic Frameworks and Their Application for 5-Hydroxymethylfurfural Synthesis

The production of 5-hydroxymethylfurfural (HMF) by the acid-catalyzed dehydration of fructose is of great significance for the comprehensive utilization of biomass resources. However, the water generated in situ not only leads to the deactivation of the active sites but also triggers the rehydration side reaction of HMF, resulting in an unsatisfactory catalytic activity and selectivity. Herein, for the first time, metal–organic frameworks (MOFs) with strong Brønsted acidity and hydrophobicity were prepared by grafting arenesulfonic acid by a diazo method. These functionalized MOFs have a large specific surface area of 1700–2600 m2/g, a high acid density of over 1.2 mmol/g, and a strong hydrophobicity with an H2O contact angle of greater than 125°. Compared with the MOF directly functionalized with sulfonic acid, the arenesulfonic acid-functionalized MOFs, which have a stronger hydrophobicity, exhibit higher activity and selectivity (up to 98.3% yield) in the transformation of fructose to HMF. Meanwhile, these arenesulfonic acid-functionalized MOFs also exhibit an excellent HMF yield for glucose and inulin reactions via the cooperative catalysis of Lewis and Brønsted acids. Furthermore, the good activity and stability of the functionalized MOFs can be maintained after recycling for five runs. The successful preparation of hydrophobic acidic MOFs provides not only an efficient catalytic system for the synthesis of HMF but also a novel, efficient route for MOF functionalization.

Fine-tuning the surface acidity of hierarchical zeolite composites for methanol-to-olefins (MTO) reaction

The zeolite nanosheet composites, containing a high acidic density ZSM-5 and weak-acidic Silicalite-1 nanosheets (Si-NS) acting as a core and a shell, respectively, have been successfully fabricated by a one-pot hydrothermal synthesis. The shell thickness, textural properties, and acidity of synthesized composites can be easily adjusted by hydrothermal synthesis time and temperature. The uniform thickness of 9.4 ± 1.1 nm of Silicalite-1 shells can be observed when using the crystallization temperature of 110 °C, whereas the non-uniform distribution of zeolite shells becomes predominant with increasing the crystallization temperature due to its rapid growing rate. Interestingly, due to the different acidity of core and shell materials, the acid site distribution of the composites has been modified with respect to their isolated zeolites, and therefore the highly selective production of propylene in MTO process is greatly improved (>90% and 50% for the hierarchical composite and unmodified ZSM-5, respectively). In addition, a significantly lower coke formation could be achieved due to the suppression of further side reactions over the stacking-layered siliceous covering on high acidic density ZSM-5 surfaces. This example opens up perspectives for the development of hierarchical zeolite composites with the modified acid surfaces for highly selective production of light olefins.

Functionalized metal–organic frameworks with strong acidity and hydrophobicity as an efficient catalyst for the production of 5-hydroxymethylfurfural

Benzenesulfonic acid -functionalized MOF with hydrophobic network and high acid density is synthesized. • A benzenesulfonic acid-functionalized MOF is prepared. • The catalyst has a strong hydrophobic network and high acid density. • 98.0% yield of HMF is obtained in the dehydration of fructose. • The sulfonated metal–organic framework is stable for recycling. In the dehydration of fructose to 5-hydroxymethyl furfural (HMF), in situ produced water weakens the acid strength of the catalyst and causes the rehydration of HMF, causing unsatisfactory catalytic activity and selectivity. In this work, a class of benzenesulfonic acid-grafted metal–organic frameworks with strong acidity and hydrophobicity is obtained by the direct sulfonation method using 4-chlorobenzenesulfonic acid as sulfonating agent. The resultant MOFs have a specific surface area of greater than 250 m 2 ·g −1 , acid density above 1.0 mmol·g −1 , and water contact angle up to 129°. The hydrophobic MOF-PhSO 3 H exhibits both higher catalytic activity and selectivity than MOF-SO 3 H in the HMF synthesis due to its better hydrophobicity and olephilicity. Moreover, the catalyst has a high recycled stability. At last, fructose is completely converted, and 98.0% yield of HMF is obtained under 120 °C in a DMSO solvent system. The successful preparation of the hydrophobic acidic MOF provides a novel hydrophobic catalyst for the synthesis of HMF.

Impact of varying starter amino acid density and energy on 42 d male Cobb MV × Cobb 500 broiler performance and processing

Summary Previous research has shown that feeding high amino acid density (AAD) diets or increased AME improved broiler performance, though the relationship between AAD and AME on performance needs to be further explored. Therefore, the objective of this study was to evaluate the impact of feeding 2 AAD and 4 AME levels from day 0 to 14 on performance and yield of 42-day-old Cobb MV × Cobb 500 males. Starter diets were formulated to medium or high AAD (HAA), and very low (VLE), low (LE), medium (ME), or high (HE) AME. Common diets were provided from day 15 to 41. A 2 × 4 factorial arrangement of treatments was used, with day 0 BW considered as a covariant. On day 0 to 14, birds receiving HAA had the lowest feed conversion ratio (FCR) corrected and uncorrected for mortality (uFCR). Birds receiving VLE diets had the highest day 0 to 14 FCR when compared to birds fed other AME levels. Feeding LE diets resulted in higher day 0 to 14 FCR when compared to ME and HE diets. An AAD × AME interaction for day 0 to 14 total Lys intake/bird found that Lys intake/bird decreased when increasing dietary AME for HAA diets. An AAD × AME interaction was observed for day 0 to 28 uFCR whereas increasing starter AAD in diets formulated to ME and HE increased day 0 to 28 uFCR; no change was observed for VLE and LE diets. However, overall performance and processing was not affected by varying starter AAD and AME levels. Further research should investigate similar feeding strategies, but in other feeding phases.

One‐Pot Synthesis of Carbon‐Based Solid Acid Polymer Catalyst: Efficient Catalysts for Liquid‐Phase Nitration of Alkanes

One‐Pot Synthesis of Carbon‐Based Solid Acid Polymer Catalyst: Efficient Catalysts for Liquid‐Phase Nitration of Alkanes

Study the Effect of Various Sulfonation Methods on Catalytic Activity of Carbohydrate-Derived Catalysts for Ester Production

In the present study, four types of sulfonation method, including thermal treatment with concentrated sulfuric acid (H2SO4), thermal decomposition of ammonium sulphate (NHSO4), thermal treatment with chlorosulfonic in chloroform (HSO3Cl), and in situ polymerization of poly(sodium4-styrenesulfonate) (PSS), were employed to convert incomplete carbonized glucose (ICG) to sulfonated heterogeneous catalysts for the fatty acid methyl ester (FAME) production. The characteristics of synthesized catalysts were further examined using Raman spectroscopy, Fourier transformation infrared (FT-IR), ammonia temperature programmed desorption (NH3-TPD), Brunauer–Emmett–Teller (BET), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX). According to experiments, the sulfonic acid density was varied in a range from 4.408 to 14.643 mmol g−1 over various sulfonation methods. The catalytic activity of synthesized catalysts over different sulfonation methods was determined by performing the conversion of palm fatty acid distillate (PFAD) to ester synthesis in a batch-system reactor. The findings reveal that using PSS-ICG resulted in the highest FAME yield of 96.3% followed by HSO3Cl-ICG of 94.8%, NHSO4-ICG of 84.2%; and H2SO4-ICG of 77.2%. According to results, the ICG sulfonated by PSS method with the highest acid density (14.643 mmol g−1) gave the highest catalytic activity over PFAD conversion to biodiesel. According to experiment results, acid density played a crucial role over FAME yield percentage. Besides acid density, it is also worth mentioning that various sulfonation methods including different mechanisms, chemicals and sulfonating agents played crucial roles in the FAME yield percentage.

Synthesis and characterization of sulfonated carbon catalysts derived from biomass waste and its evaluation in glycerol acetylation

Sulfonated carbon catalysts were synthesized from palm kernel shell biomass using direct, chemical and template methods of carbonization under CO2 environment at 400 and 800 °C respectively and subsequently functionalized with concentrated sulfuric acid. The precursor material and the synthesized catalysts were characterized by proximate analysis, CHNS, XRD, FTIR, TPD, TGA, SEM, N2 adsorption isotherm, BET surface area, and acid-base titration. The synthesized acid catalysts were evaluated in glycerol acetylation with acetic acid (molar ratio 1:6) in a batch liquid phase reaction under atmospheric pressure at 120 °C, 450 rpm for 1 h, 3 h, and 5 h respectively. The performance was compared with commercial Amberlyst-15 catalysts and homogeneous concentrated sulfuric acid. Of all the synthesized catalysts, the catalyst obtained from the template method carbonized at 800 °C showed the highest selectivity to triacetin (58.9%) with over 97% glycerol conversion within a 3-h reaction time. The selectivity to monoacetin and diacetin was 5.8 and 32.2% respectively. The catalytic activity of the catalyst was attributed to the synergistic effect of good physicochemical characteristics including textural properties and high acidic site density.

An alumina‐coated UiO‐66 nanocrystalline solid superacid with high acid density as a catalyst for ethyl levulinate synthesis

AbstractBACKGROUNDThe zirconium‐containing metal–organic framework (MOF) UiO‐66 was used as a cell to synthesize SO42−/ZrO2@Al2O3, a high‐density superacid with relatively strong Brønsted acidity. The UiO‐66 MOF was first coated with alumina to form ZrO2@Al2O3. Impregnation with ammonium sulfate and calcination at 500 °C afforded the bimetallic composite solid superacid SO42−/ZrO2@Al2O3.RESULTSScanning and transmission electron microscopy images confirmed that UiO‐66 was successfully coated with aluminium oxide, and its octahedral structure and uniform size (400–600 nm) were retained. SO42−/ZrO2@Al2O3 had a Brunauer–Emmett–Teller specific surface area of 301–330 m2 g−1 and average pore diameter of 9.6–10.7 nm. X‐ray photoelectron spectroscopy and Fourier transform infrared analysis showed that SO42−/ZrO2@Al2O3 contained S6+ and Al3+. Temperature‐programmed ammonia desorption analysis showed that SO42−/ZrO2@Al2O3 contained super‐strong acid sites. The total volume of desorbed ammonia reached 90–109 cm3 g−1. Infrared spectra of adsorbed pyridine indicated that SO42−/ZrO2@Al2O3 contained mainly Lewis acid sites and was relatively rich in Brønsted acid sites. Thermogravimetric analysis showed that the thermal stability of SO42−/ZrO2@Al2O3 was high.CONCLUSIONSSO42−/ZrO2@Al2O3‐3M (the impregnation concentration of ammonium sulfate was 3 mol L−1) and glucose were used to synthesize ethyl levulinate (EL) in ethanol. The highest EL yield of 37.5 mol% was obtained after reacting the mixture at 200 °C for 5 h. An EL yield of 28.8 mol% was obtained after four consecutive reuses of the SO42−/ZrO2@Al2O3‐3M catalyst. © 2020 Society of Chemical Industry

Polyphenylene-Based Solid Acid as an Efficient Catalyst for Activation and Hydration of Alkynes.

Porous polymer catalysts possess the potential to combine the advantages of heterogeneous and homogeneous catalysis, namely, easy postreaction recycling and high dispersion of active sites. Here, we designed a −SO3H functionalized polyphenylene (PPhen) framework with purely sp2-hybridized carbons, which exhibited high activity in the hydration of alkynes including challenging aliphatic substrates such as 1-octyne. The superiority of the structure lies in its covalent crosslink in the xy-plane with a π–π stacking interaction between the planes, enabling simultaneously high swellability and porosity (653 m2·g–1). High acidic site density (2.12 mmol·g–1) was achieved under a mild sulfonation condition. Similar turnover frequencies (0.015 ± 0.001 min–1) were obtained regardless of acidic density and crosslink content, suggesting high accessibility for all active sites over PPhen. In addition, the substituted benzene groups can activate alkynes through a T-shape CH/π interaction, as indicated by the 8 and 16 cm–1 red shift of the alkyne C–H stretching peak for phenylacetylene and 1-octyne, respectively, in the infrared (IR) spectra. These advantages render PPhen-SO3H a promising candidate as a solid catalyst replacing the highly toxic liquid phase acids such as the mercury salt.